Optical wavelength multiplexing system, optical wavelength multiplexing method, and computer product

ABSTRACT

An optical wavelength multiplexing system includes transmission-side and reception-side optical wavelength multiplexers, and terminal devices, which are connected to each other by optical fiber cables. Optical wavelength converters in the transmission-side optical wavelength multiplexers are connected to ports respectively. The optical wavelength converter converts an input optical signal into an arbitrary preset wavelength to generate a converted optical signal. The port has a predetermined wavelength preset therein. Each optical power level of input converted optical signals is compared with each optical power level of optical signals of respective wavelengths set in the ports. When a difference is detected in the comparison result, it is determined that an optical wavelength converter is incorrectly connected to the port.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for an optical wavelengthmultiplexing system, an optical wavelength multiplexing method, and acomputer product.

2. Description of the Related Art

High volume data such as images and moving images is transmitted morefrequently than ever before with the spread of the Internet. To transmitsuch high volume data at high speed, a network line using x DigitalSubscriber Line (xDSL) technology enabling high-speed networkcommunication is generally and frequently used. Recently, however, anoptical network which is a higher speed network such as Fiber To TheHome (FTTH) using an optical fiber cable is also used.

As a technology of effectively using the optical fiber cable, wavelengthdivision multiplexing (WDM) draws attention. The WDM is a technology fortransmitting a plurality of signals having different wavelengths overone optical fiber cable. Specifically, this technology increasestransmission capacity of the optical fiber cable by simultaneously usingthe optical signals having different wavelengths.

In an optical wavelength multiplexing system including an Optical Addand Drop Multiplexer (OADM) that adds an optical signal having anarbitrary wavelength and drops and receives the optical signal using theWDM, individual frequencies are assigned to a plurality of portsrespectively. An optical wavelength converter that converts (outputs) aninput optical signal into an optical signal having an assigned frequencyis connected to each of the ports.

Specifically, optical wavelength converters that output assignedfrequencies need to be correctly connected to the ports respectively.However, because the number of optical wavelengths to be multiplexed inthe OADM increases in recent years, the OADM is caused to have manyports. As a result, there occur many cases of causing an incorrectconnection. The incorrect connection indicates that an opticalwavelength converter outputs a wavelength different from the wavelengthassigned to the connected port and available for optical wavelengthdivision multiplexing. Hence, various technologies for detecting such anincorrect connection are disclosed.

Japanese Patent Application Laid-Open No. 2004-32088 discloses atechnology of detecting the incorrect connection by using awavelength-dependent arrayed waveguide grating (AWG) in multiplexingoptical wavelengths. Specifically, the AWG having the wavelengthdependency has a characteristic that, even when an optical signal havinga wavelength different from the wavelength assigned to each port isinput, a passing of the optical signal through the AWG is prevented. Byusing this characteristic, the incorrect connection is detected based ona comparison of an optical power level at each port of the AWG to whichthe wavelength is assigned with an optical power level aftermultiplexing and branching optical signals having different wavelengthsinput through the ports. Specifically, when there is any port which isincorrectly connected, an error is presented between optical powerlevels before and after the multiplexing of the optical signals.Therefore, by detecting the error, the incorrect connection in each portis detected.

However, the conventional technology has a problem that the arrayedwaveguide grating (AWG) is very expensive, thereby causing the cost forconstructing the optical wavelength multiplexing system to increase.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to one aspect of the present invention, an optical wavelengthmultiplexing system includes a plurality of optical wavelengthconverters that convert input optical signals into arbitrary presetwavelengths and generate converted optical signals respectively; aplurality of ports in which predetermined wavelengths are preset and towhich the optical wavelength converters are connected respectively; aplurality of first optical-power-level detectors that are connected tothe ports respectively, and detect optical power levels of the convertedoptical signals input into the ports respectively; an optical signalmultiplexer that multiplexes all the converted optical signals inputfrom the ports to generate a multiplexed optical signal, the generatedmultiplexed optical signal being transmitted to a receiving device inthe optical wavelength multiplexing system and demultiplexed intooptical signals of predetermined wavelengths; a plurality of input unitsthat are provided in the ports respectively and input the convertedoptical signals input into the ports, into the optical signalmultiplexer; an input controller that controls each of the input unitsso as not to input the converted optical signal into the optical signalmultiplexer until an optical power level of the converted optical signalis detected by the first optical-power-level detector, and also controlseach of the input units so as to input the converted optical signal intothe optical signal multiplexer when the optical power level of theconverted optical signal is detected; a second optical-power-leveldetector that detects, from the multiplexed optical signal, each opticalpower level of the predetermined wavelengths set in the ports after theconverted optical signals are multiplexed; and an incorrect connectiondetector that compares each optical power level of the converted opticalsignals detected by the first optical-power-level detector with eachoptical power level of the predetermined wavelengths detected by thesecond optical-power-level detector, and detects that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result.

According to another aspect of the present invention, an opticalwavelength multiplexing method is used in an optical wavelengthmultiplexing system where a plurality of optical wavelength converterswhich convert input optical signals into arbitrary preset wavelengthsand generate converted optical signals respectively, are respectivelyconnected to a plurality of ports in which predetermined wavelengths arepreset, and where the converted optical signals are multiplexed in atransmitting device and transmitted to a receiving device to bedemultiplexed into optical signals of predetermined wavelengths. Theoptical wavelength multiplexing method includes detecting each opticalpower level of the converted optical signals input into the ports;multiplexing all the converted optical signals input from the ports togenerate a multiplexed optical signal; inputting the converted opticalsignals input into the ports for the multiplexing; controlling theinputting so as not to input the converted optical signal for themultiplexing until an optical power level of the converted opticalsignal is detected in the detecting, and also controlling the inputtingso as to input the converted optical signal for the multiplexing whenthe optical power level of the converted optical signal is detected;detecting, from the multiplexed optical signal, each optical power levelof the predetermined wavelengths set in the ports after the convertedoptical signals are multiplexed; and comparing each optical power levelof the converted optical signals detected in the detecting of eachoptical power level of the converted optical signals with each opticalpower level of the predetermined wavelengths detected in the detectingof each optical power level of the predetermined wavelengths after theconverted optical signals are multiplexed, and detecting that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result.

According to still another aspect of the present invention, acomputer-readable recording medium stores therein a computer programthat implements the above method on a computer.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an overview and characteristics of an opticalwavelength multiplexing system according to a first embodiment;

FIG. 2 is a block diagram of a configuration of the optical wavelengthmultiplexing system according to the first embodiment;

FIG. 3 is a diagram of an example of information stored in a memoryunit;

FIG. 4 is a flowchart of a process of detecting an incorrect connectionin the optical wavelength multiplexing system according to the firstembodiment;

FIG. 5 is a schematic of an overall configuration of an opticalwavelength multiplexing system according to a second embodiment;

FIG. 6 is a schematic of an overall configuration of an opticalwavelength multiplexing system according to a third embodiment;

FIG. 7 is a schematic of an overall configuration of an opticalwavelength multiplexing system according to a fourth embodiment; and

FIG. 8 is a flowchart of a process of determining an incorrectconnection and a process for informing about a destination in an opticalwavelength multiplexing system according to a fifth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention will be explained indetail below with reference to the accompanying drawings. It should benoted that key terms used in the following embodiments, an overview andcharacteristics of an optical wavelength multiplexing system accordingto a first embodiment, a configuration and a procedure in the opticalwavelength multiplexing system according to the first embodiment, andadvantages of the first embodiment will be explained in this order, andthen other embodiments will be explained.

At first, the key terms used in the embodiments will be explained below.The “optical wavelength multiplexing system” indicates a system thatrealizes an optical communication network. The system includes atransmission-side optical wavelength multiplexer and a reception-sideoptical wavelength multiplexer. The system allows an increase intransmission capacity of an optical fiber cable by transmitting aplurality of signals having different wavelengths over the optical fibercable for connecting between the transmission side and the receptionside, namely, by simultaneously using the plurality of optical signalshaving different wavelengths. It should be noted that the “opticalwavelength multiplexing system” corresponds to “optical wavelengthmultiplexing system” in claims.

The transmission-side optical wavelength multiplexer causes opticalwavelength converters to convert optical signals input from terminaldevices into arbitrary wavelengths respectively, and causes an opticalwavelength multiplexing unit to multiplex the converted optical signals.The transmission-side optical wavelength multiplexer further causes atransmission-light amplifying unit to amplify the multiplexed opticalsignal to an optical level at which the optical signal can betransmitted, and transmit the optical signal of that level to thereception-side optical wavelength multiplexer.

The reception-side optical wavelength multiplexer causes areceived-light amplifying unit to amplify the multiplexed optical signaldegraded during the transmission from the transmission-side opticalwavelength multiplexer, and causes an optical wavelength demultiplexingunit to demultiplex the multiplexed optical signal into thepredetermined wavelengths before being multiplexed. The reception-sideoptical wavelength multiplexer further causes optical wavelengthconverters to reversely convert the demultiplexed optical signals intorespective original signals and transmit the original signals to theterminal devices, respectively.

Each of the optical wavelength multiplexing unit in thetransmission-side optical wavelength multiplexer and the opticalwavelength demultiplexing unit in the reception-side optical wavelengthmultiplexer has a plurality of ports to be connected to the opticalwavelength converters. An input wavelength is previously set in each ofthe ports, and a wavelength to be converted is previously set in each ofthe optical wavelength converters connected to the corresponding port soas to be converted to the wavelength set in a destination port.

Accordingly, the transmission-side optical wavelength multiplexerreceives the optical signals converted to the respective presetwavelengths, multiplexes the converted optical signals, and transmitsthe multiplexed optical signal. The reception-side optical wavelengthmultiplexer receives and demultiplexes the multiplexed optical signalinto optical signals having the original wavelengths, to obtain theoptical signals. Even when any one of the optical signals having adifferent wavelength from the wavelength set in the corresponding portis received, the transmission-side optical wavelength multiplexermultiplexes the optical signals including the improper optical signal,and transmits a multiplexed optical signal. However, when receiving anddemultiplexing the multiplexed optical signal, the reception-sideoptical wavelength multiplexer cannot normally demultiplex themultiplexed optical signal.

Although the transmission-side optical wavelength multiplexer and thereception-side optical wavelength multiplexer are explained below asseparate devices for convenience in an explanation in the embodiments,the present invention is not limited to such a configuration. Therefore,the reception-side optical wavelength multiplexer explained in theembodiments may transmit a multiplexed optical signal. In other words,it does not matter which is which, because the device that transmits amultiplexed optical signal is set as a transmission-side opticalwavelength multiplexer while the device that receives the multiplexedoptical signals is set as a reception-side optical wavelengthmultiplexer.

The “terminal device” indicates a device that transmits an opticalsignal to the optical wavelength multiplexing system and receives anoptical signal therefrom. Specifically, the terminal device is connectedto an optical wavelength converter that converts an optical signal intoan arbitrary preset wavelength. The optical signal transmitted by theterminal device is converted into an arbitrary wavelength by the opticalwavelength converter, and a converted optical signal is input into acorresponding port in the transmission-side optical wavelengthmultiplexer.

FIG. 1 is a schematic of an overview and characteristics of an opticalwavelength multiplexing system according to a first embodiment.

As shown in FIG. 1, the optical wavelength multiplexing system includesthe transmission-side optical wavelength multiplexer, the reception-sideoptical wavelength multiplexer, and terminal devices 1 to 3, which areconnected to each other through optical fiber cables so as to enablecommunications with each other. In the transmission-side opticalwavelength multiplexer, each of a plurality of optical wavelengthconverters converts an input optical signal into an arbitrary presetwavelength to generate a converted optical signal. The opticalwavelength converters are connected to a plurality of ports whosepredetermined wavelengths are set in advance, respectively.

Specifically, wavelengths λ1 to λ3 are set in a port A to a port C,respectively. The port A with the wavelength λ1 set therein is connectedto an optical wavelength converter that converts an input optical signalinto an optical signal of the wavelength λ1. The port B with thewavelength λ2 set therein is connected to another optical wavelengthconverter that converts an input optical signal into the wavelength λ3.In this case, although the port B is supposed to be connected to stillanother optical wavelength converter that converts an input opticalsignal into the wavelength λ2, the optical wavelength converter thatconverts the optical signal into the wavelength λ3 is incorrectlyconnected to the port B.

As explained above, the optical wavelength multiplexing system accordingto the first embodiment configured in the above manner multiplexes theconverted optical signals generated by the optical wavelengthconverters, and generates and transmits the multiplexed optical signal.At the same time, the system demultiplexes the received multiplexedoptical signal into the optical signals of the respective predeterminedwavelengths. Particularly, this system has main characteristics suchthat an incorrect connection can be detected and the cost forconstructing the system can be reduced.

The main characteristics will be more specifically explained below. Thetransmission-side optical wavelength multiplexer controls each of inputunits 1 to 3 so as not to input a converted optical signal into anoptical multiplexer until the optical power level of the convertedoptical signal is detected. The optical wavelength converter in thetransmission-side optical wavelength multiplexer receives the opticalsignal transmitted from the terminal device 1, converts the opticalsignal into an optical signal having the wavelength λ1, and outputs theconverted optical signal to the port A (see (1) and (2) of FIG. 1).

Optical power level detectors 1 to 3 in the transmission-side opticalwavelength multiplexer detect the optical power levels of the convertedoptical signals input into the ports, respectively (see (3) of FIG. 1).Specifically, the optical power level detector 1 detects the opticalpower level of the converted optical signal having the wavelength λ1input into the port A.

Subsequently, when the optical power level of the converted opticalsignal is detected, the transmission-side optical wavelength multiplexercontrols each of the input units 1 to 3 so as to input the convertedoptical signal into the optical multiplexer (see (4) of FIG. 1).Specifically, when the optical power level of the converted opticalsignal input into the port A is detected, an input controller in thetransmission-side optical wavelength multiplexer controls the input unit1 so as to input the converted optical signal into the opticalmultiplexer.

The transmission-side optical wavelength multiplexer inputs theconverted optical signals input to the ports into the opticalmultiplexer, multiplexes all the converted optical signals input fromthe ports to generate a multiplexed optical signal (see (5) and (6) ofFIG. 1). Specifically, the transmission-side optical wavelengthmultiplexer inputs the converted optical signal which is input into theport A and converted into the wavelength λ1, into the opticalmultiplexer, and the optical multiplexer multiplexes all the inputconverted optical signals to generate and output a multiplexed opticalsignal to the transmission-light amplifying unit.

Thereafter, the transmission-side optical wavelength multiplexerbranches the multiplexed optical signal, and detects optical powerlevels of the predetermined wavelengths set in the respective ports ofthe branched optical signal, from the branched multiplexed opticalsignal (see (7) and (8) of FIG. 1). Specifically, an optical branchingunit in the transmission-side optical wavelength multiplexer branchesthe multiplexed optical signal, and an optical power level detectorprovided therein detects an optical power level of the wavelength λ1 setin the port A of the branched optical signal, from the branchedmultiplexed optical signal.

The transmission-side optical wavelength multiplexer compares eachdetected optical power level of the converted wavelengths with eachdetected optical power level of the wavelengths of the branched opticalsignal. When a difference is detected in the comparison result, then thetransmission-side optical wavelength multiplexer detects that aparticular optical wavelength converter is incorrectly connected to aport because the optical wavelength converter converts the opticalsignal into a wavelength different from the predetermined wavelength setin the port (see (9) of FIG. 1).

Specifically, an incorrect connection detector in the transmission-sideoptical wavelength multiplexer compares an optical power level of thewavelength which is converted into the wavelength λ1 and input into theport A with an optical power level of the wavelength λ1 set in the portA, after branching the multiplexed optical signal multiplexed by theoptical multiplexer, from the branched multiplexed optical signal.Subsequently, the transmission-side optical wavelength multiplexerdetermines that both detected optical signals, i.e., one optical signalhaving the optical power level of the converted wavelength and the otherhaving the optical power level of the wavelength of the branched opticalsignal, are the same optical wavelengths converted into the wavelengthλ1. Based on this determination, the transmission-side opticalwavelength multiplexer determines that there is no difference in the twooptical power levels, and that the optical wavelength converter thatconverts the optical signal into the wavelength λ1 is correctlyconnected to the port A in which the wavelength λ1 is set.

Similarly to the method described above, when an optical signal istransmitted from the terminal device 2, the transmission-side opticalwavelength multiplexer determines whether an optical wavelengthconverter connected to the terminal device 2 is connected to an improperport.

Specifically, the optical wavelength converter in the transmission-sideoptical wavelength multiplexer that receives the optical signal from theterminal device 2, converts the optical signal into an optical signalhaving a wavelength λ3, and outputs the converted optical signal to theport B. The optical power level detector 2 detects the optical powerlevel of a converted optical signal having the wavelength λ3 input intothe port B (see (10) to (12) of FIG. 1).

When the optical power level of the converted optical signal isdetected, the transmission-side optical wavelength multiplexer controlsthe input unit 2 so as to input the converted optical signal into theoptical multiplexer, inputs the converted optical signals input to theport A and the port B respectively into the optical multiplexer, andmultiplexes all the converted optical signals input from the port A andthe port B to generate a multiplexed optical signal. Thetransmission-side optical wavelength multiplexer branches themultiplexed optical signal, and detects the optical power level of thewavelength λ2 set in the port B, from the branched optical signal (see(13) to (17) of FIG. 1).

The incorrect connection detector in the transmission-side opticalwavelength multiplexer compares the detected optical power level afterconversion with the detected optical power level after branching. When adifference is detected in the comparison result, the incorrectconnection detector detects that an optical wavelength converter isincorrectly connected to the port B because the optical wavelengthconverter converts the optical wavelength into a wavelength differentfrom the wavelength λ2 set in the port B (see (18) of FIG. 1).

Specifically, the incorrect connection detector compares theoptical-power level of the wavelength which is converted into thewavelength λ3 and input into the port B, with the optical power level ofthe wavelength λ2 set in the port B, from the branched multiplexedoptical signal. The incorrect connection detector detects that theoptical power levels show a difference in wavelength, and therebydetects the difference in the both optical power levels. Then, theincorrect connection detector detects that the optical wavelengthconverter which converts the optical signal into a wavelength differentfrom the wavelength λ2 set in the port B is incorrectly connected to theport B.

In the example described above, the case where the incorrect connectionis detected from the optical signal in-put into the port A, and thendetected from the optical signal input into the port B is explained.However, the present invention is not limited to this configuration, andmay be configured that the incorrect connections are detected from theoptical signals simultaneously input into the port A and the port B.

As explained above, in the optical wavelength multiplexing systemaccording to the first embodiment, the optical wavelength convertersconvert input optical signals into arbitrary preset wavelengths togenerate converted optical signals respectively, and the opticalwavelength converters are connected to the ports in which respectivepredetermined wavelengths are preset. The incorrect connection can bedetected in the above manner when the converted optical signals aremultiplexed to generate and transmit a multiplexed optical signal, andthe cost for constructing the system can be reduced.

FIG. 2 is a block diagram of the configuration of the optical wavelengthmultiplexing system according to the first embodiment. As shown in FIG.2, the optical wavelength multiplexing system includes atransmission-side optical wavelength multiplexer 10 and a reception-sideoptical wavelength multiplexer 70.

The transmission-side optical wavelength multiplexer 10 includes amemory unit 11, optical wavelength converters 12 to 14, an opticalwavelength multiplexing unit 20, a transmission-light amplifying unit40, an optical spectrum monitor 50, and an optical-level monitoringcontroller 60.

The memory unit 11 stores therein wavelengths set in a port A 21 to aport C 23 which will be explained later. Specifically, as shown in FIG.3, the memory unit 11 stores therein “Port A, λ1”, “Port B, λ2”, “PortC, λ3”, and so on as to indicate “a port number specifying a port and awavelength showing a wavelength to be set”. FIG. 3 is a diagram of anexample of information stored in the memory unit.

Each of the optical wavelength converters 12 to 14 converts an inputoptical signal into an arbitrary wavelength which is set in advance.Specifically, λ1, λ2, and the like are set, in advance by a user, in theoptical wavelength converters 12 to 14 as wavelengths to be convertedrespectively, and the optical wavelength converters 12 to 14 convert theinput optical signals into optical signals having the preset wavelengthssuch as λ1, λ2, and the like, respectively. As one example, thewavelength λ1 is set in the optical wavelength converter 12, thewavelength λ3 is set in the optical wavelength converter 13, and thewavelength λ2 is set in the optical wavelength converter 14.

The optical wavelength multiplexing unit 20 includes the ports A 21 to C23, photodetectors (PD) 24 to 26, optical switches 27 to 29, and anoptical coupler (CPL) 30 as elements closely related to the presentinvention in particular. The optical wavelength multiplexing unit 20performs various controls so as to multiplex the converted opticalsignals input into the ports from the optical wavelength converters 12to 14 respectively, generate a multiplexed optical signal, and transmitthe generated multiplexed optical signal to the transmission-lightamplifying unit 40 to be explained later.

Predetermined wavelengths are set in advance and converted opticalsignals converted by the optical wavelength converters 12 to 14 areinput in the port A 21 to port C 23, respectively, and the convertedoptical signals are output to the PD 24 to PD 26 to be explained later,respectively. Specifically, the optical wavelength converter 12 with thewavelength λ1 set therein and the PD 24 are connected to the port A 21,the optical wavelength converter 13 with the wavelength λ3 set thereinand the PD 25 are connected to the port B 22, and the optical wavelengthconverter 14 with the wavelength λ2 set therein and the PD 26 areconnected to the port C 23. An optical signal converted into thewavelength λ1 by the optical wavelength converter 12 is input into theport A 21, and the converted optical signal is output to the PD 24.Similarly, an optical signal converted into the wavelength λ3 by theoptical wavelength converter 13 is input into the port B 22, and theconverted optical signal is output to the PD 25. An optical signalconverted into the wavelength λ2 by the optical wavelength converter 14is input into the port C 23, and the converted optical signal is outputto the PD 26.

Although the case where three ports such as the port A 21 to port C 23are provided is explained, the present invention is not limited to thisconfiguration. Therefore, four ports may be provided, and thus there isno limitation in the number of the ports. Furthermore, opticalwavelength converters of the same number as the ports may be connectedto the ports respectively, or one optical wavelength converter may beconnected to a plurality of ports. When one optical wavelength converteris connected to a plurality of ports, because different wavelengths areset in the ports, the optical wavelength converter is caused to set aplurality of optical wavelengths therein, converts optical signals intodifferent wavelengths, and inputs the converted optical signals into theports, respectively.

The PD 24 to PD 26 are circuits such as large scale integration (LSI)which are connected to the ports respectively and detect optical powerlevels of the converted optical signals input into the portsrespectively. Specifically, the PD 24 is connected to the port A 21,receives the optical signal converted into the wavelength λ1 by theoptical wavelength converter 12 from the port A 21, detects the opticalpower level of the input converted optical signal, and informs theoptical-level monitoring controller 60 to be explained later of thedetected optical power level. Similarly, the PD 25 is connected to theport B 22, receives the optical signal converted into the wavelength λ3by the optical wavelength converter 13 from the port B 22, detects theoptical power level of the input converted optical signal, and informsthe optical-level monitoring controller 60 of the detected optical powerlevel. The PD 26 is connected to the port C 23, receives the opticalsignal converted into the wavelength λ2 by the optical wavelengthconverter 14 from the port C 23, detects the optical power level of theinput converted optical signal, and informs the optical-level monitoringcontroller 60 of the detected optical power level. It should be notedthat the PD 24 to PD 26 correspond to “first optical-power-leveldetector” in claims.

The optical switches 27 to 29 input the converted optical signals inputinto the ports respectively, into the optical coupler 30 to be explainedlater. Specifically, when the optical-level monitoring controller 60 tobe explained later controls the optical switch 27 so as to input theconverted optical signal into the optical coupler 30, the optical switch27 inputs the optical signal which is converted into the wavelength λ1and input from the PD 24, into the optical coupler 30. Similarly, theoptical switch 28 inputs the optical signal which is converted into thewavelength λ3 and input from the PD 25, into the optical coupler 30. Theoptical switch 29 inputs the optical signal which is converted into thewavelength λ2 and input from the PD 26, into the optical coupler 30.

Here, because the wavelength λ2 is set in the port B 22, the opticalsignal converted into the wavelength λ2 is supposed to be input into theoptical switch 28 via the PD 25 in a normal situation. However, in thisexample, the optical wavelength converter 13 that converts the opticalsignal into the wavelength λ3 is connected to the port B 22, whichresults in the case where the optical signal converted into thewavelength λ3 is input into the optical switch 28. Despite this fact,the optical switches 27 to 29, which only have a function oftransmitting optical signals, inputs the converted optical signals intothe optical coupler 30 even if any one of the optical signals isconverted into an erroneous wavelength. Although the case where threeoptical switches are provided is explained in the present example, thepresent invention is not limited to this configuration, and thus, theoptical wavelength multiplexing system has optical switches of the samenumber as the ports. It should be noted that the optical switches 27 to29 correspond to “input units” in claims.

The optical coupler 30 multiplexes all the converted optical signalsinput from a plurality of ports to generate a multiplexed opticalsignal. Specifically, when receiving the optical signals which areconverted into the wavelengths λ1 to λ3 and input from the port A 21 toport C 23 via the optical switches 27 to 29 respectively, the opticalcoupler 30 multiplexes all the input converted optical signals, andoutputs the multiplexed optical signal to the transmission-lightamplifying unit 40 to be explained later. Even when the optical signalconverted into a wavelength different from the wavelength set in each ofthe ports is input into the optical coupler 30, the optical coupler 30multiplexes all the input converted optical signals and outputs themultiplexed optical signal to the transmission-light amplifying unit 40.It should be noted that the optical coupler 30 corresponds to “opticalsignal multiplexer” in claims.

The transmission-light amplifying unit 40 includes a PD 41, an opticalbranching unit 42, and an optical amplifier 43 as elements closelyrelated to the present invention in particular. The transmission-lightamplifying unit 40 amplifies the multiplexed optical signal input intothe PD 41 and transmits the amplified optical signal to thereception-side optical wavelength multiplexer 70. The PD 41 is a circuitsuch as an LSI that outputs the multiplexed optical signal output fromthe optical wavelength multiplexing unit 20 to the optical branchingunit 42 to be explained later. Specifically, the PD 41 receives themultiplexed optical signal output from the optical coupler 30 in theoptical wavelength multiplexing unit 20 and outputs the multiplexedoptical signal to the optical branching unit 42.

The optical branching unit 42 branches the multiplexed optical signalmultiplexed by the optical coupler 30. Specifically, the opticalbranching unit 42 receives the multiplexed optical signal via the PD 41,branches the multiplexed optical signal into the optical spectrummonitor 50 and the optical amplifier 43 to be explained later, andoutputs the multiplexed optical signal to both of them respectively. Itshould be noted that the optical branching unit 42 corresponds to“optical branching unit” in claims.

The optical amplifier 43 amplifies the multiplexed optical signal to anoptical level at which the multiplexed optical signal can betransmitted, and transmits the amplified optical signal to thereception-side optical wavelength multiplexer 70. Specifically, theoptical level of the input multiplexed optical signal after beingbranched by the optical branching unit 42 is degraded to about one halfthereof, and the signal cannot be transmitted. Therefore, the opticalamplifier 43 amplifies the multiplexed optical signal, branched andinput by the optical branching unit 42 to an optical level at which itcan be transmitted (e.g., to about twice of the input level), andtransmits the amplified optical signal to the reception-side opticalwavelength multiplexer 70.

The optical spectrum monitor 50 detects each optical power level of thepredetermined wavelengths set in the ports, from the multiplexed opticalsignal branched by the optical branching unit 42. Specifically, theoptical spectrum monitor 50 detects the optical power level of thewavelength λ1 set in the port A 21 from the multiplexed optical signalbranched by the optical branching unit 42, and transmits the detectedoptical power level to the optical-level monitoring controller 60 to beexplained later. Similarly, the optical spectrum monitor 50 detects theoptical power level of the wavelength λ2 set in the port B 22 after themultiplex, and transmits the detected optical power level to theoptical-level monitoring controller 60. The optical spectrum monitor 50detects the optical power level of the wavelength λ3 set in the port C23 after the multiplex, and transmits the detected optical power levelto the optical-level monitoring controller 60. It should be noted thatthe optical spectrum monitor 50 correspond to “secondoptical-power-level detector” in claims.

The optical-level monitoring controller 60 controls the optical switches27 to 29 so as not to input the converted optical signals into theoptical coupler 30 until optical power levels of the convertedwavelengths are detected by the PD 24 to PD 26, respectively. When eachoptical power level of the converted wavelengths is detected by the PD24 to PD 26, the optical-level monitoring controller 60 controls theoptical switches 27 to 29 so as to input the converted optical signalsinto the optical coupler 30. Then, the optical-level monitoringcontroller 60 compares each optical power level of the convertedwavelengths detected by the PD 24 to PD 26 with each optical power levelof the wavelengths of the branched optical signal detected by theoptical spectrum monitor 50. When a difference is detected in thecomparison result, the optical-level monitoring controller 60 detectsthat an optical wavelength converter is incorrectly connected to a portbecause the optical wavelength converter converts the wavelength into awavelength different from the predetermined wavelength set in the port.

Specifically, the optical-level monitoring controller 60 stops theoptical switches 27 to 29 so as not to input the converted opticalsignals into the optical coupler 30 until the PD 24 to PD 26 detect theoptical power levels of the converted wavelengths respectively. When theoptical power levels of the converted wavelengths are detected by the PD24 to PD 26 respectively, the optical-level monitoring controller 60controls the optical switches 27 to 29 so as to input the convertedoptical signals into the optical coupler 30.

The optical-level monitoring controller 60 compares the optical powerlevel of the wavelength λ1 detected by the PD 24 after the conversion,with the optical power level of the wavelength λ1 set in the port A 21of the branched optical signal, detected by the optical spectrum monitor50. As a result of the comparison, both of the optical power levels aredetected as those of optical wavelengths converted into the wavelengthλ1, which indicates there is no difference between the two optical powerlevels. Therefore, it is determined that the optical wavelengthconverter is correctly connected to the port A 21 with the wavelength λ1set therein because the converter converts the optical signal into thewavelength λ1.

The optical-level monitoring controller 60 also compares the opticalpower level of the wavelength λ3 detected by the PD 25 after theconversion, with the optical power level of the wavelength λ2 set in theport B 22 of the branched optical signal, detected by the opticalspectrum monitor 50. As a result of the comparison, the optical powerlevels are detected as those of different wavelengths, and a differenceis detected from both of the optical power levels. Thus it is determinedthat the optical wavelength converter is incorrectly connected to theport B 22 because the converter converts the optical signal to awavelength different from the wavelength λ2 set in the port B 22.

Similarly, the optical-level monitoring controller 60 compares theoptical power level of the wavelength λ2 detected by the PD 26 after theconversion, with the optical power level of the wavelength λ3 set in theport C 23 of the branched optical signal, detected by the opticalspectrum monitor 50. As a result of the comparison, the optical powerlevels are detected as those of different wavelengths, and a differenceis detected from both of the optical power levels. Thus it is determinedthat the optical wavelength converter is incorrectly connected to theport C 23 because the converter converts the optical signal to awavelength different from the wavelength λ3 set in the port C 23. Itshould be noted that the optical-level monitoring controller 60corresponds to “input controller” and “incorrect connection detector” inclaims.

The reception-side optical wavelength multiplexer 70 includes a memoryunit 71, a received-light amplifying unit 72, an optical wavelengthdemultiplexing unit 74, optical wavelength converters 82 to 84, and anoptical level monitor 85. Similarly to the memory unit 11 in thetransmission-side optical wavelength multiplexer 10, the memory unit 71stores therein wavelengths set in the port A 21 to the port C 23 in thetransmission-side optical wavelength multiplexer 10 as wavelengths setin a port A 79 to a port C 81 to be explained later. Specifically, thememory unit 71 stores therein “port A, λ1”, “port B, λ2”, “port C, λ3”,and so on (see FIG. 3).

The received-light amplifying unit 72 includes an optical amplifier 73as an element closely related to the present invention in particular,and amplifies a received multiplexed optical signal. The opticalamplifier 73 amplifies a degraded multiplexed optical signal.Specifically, because the optical power level of the multiplexed opticalsignal is degraded during the transmission from the transmission-sideoptical wavelength multiplexer 10, the optical amplifier 73 amplifiesthe optical power level to recover the multiplexed optical signal.

The optical wavelength demultiplexing unit 74 controls so as todemultiplex the received multiplexed optical signal. The opticalwavelength demultiplexing unit 74 includes a received-light wavelengthdemultiplexer (AWG) 75, PDs 76 to 78, and the port A 79 to port C 81 aselements closely related to the present invention in particular. Thereceived-light wavelength demultiplexer 75 demultiplexes the multiplexedoptical signal into the original wavelengths. Specifically, when themultiplexed optical signal transmitted from the transmission-sideoptical wavelength multiplexer 10 is amplified by the received-lightamplifying unit 72 and is input into the received-light wavelengthdemultiplexer 75, the received-light wavelength demultiplexer 75demultiplexes the multiplexed optical signal, to obtain the opticalsignals having the wavelengths λ1 to λ3 (which are stored in the memoryunit 11) set in the port A 21 to the port C 23 respectively in thetransmission-side optical wavelength multiplexer 10.

The PDs 76 to 78 are circuits such as LSIs that are connected to aplurality of ports respectively and detect the optical power levels ofdemultiplexed optical signals respectively. Specifically, when themultiplexed optical signal is demultiplexed by the received-lightwavelength demultiplexer 75 and the demultiplexed optical signals havingthe wavelengths λ1 to λ3 are obtained, each of the PDs 76 to 78 detectseach optical power level of the demultiplexed optical signals andoutputs the detected optical power level to the optical level monitor 85to be explained later.

The port A 79 to port C 81 have respective predetermined wavelengthspreset therein, and receive the demultiplexed optical signalsdemultiplexed by the received-light wavelength demultiplexer 75, andoutput the demultiplexed optical signals to the optical wavelengthconverters 82 to 84 to be explained later, respectively. Specifically,the wavelength λ1 which is the same as that of the port A 21 in thetransmission-side optical wavelength multiplexer 10 is set in the port A79. The port A 79 receives the demultiplexed optical signal of thewavelength λ1 demultiplexed by the received-light wavelengthdemultiplexer 75 via the PD 76, and outputs the demultiplexed opticalsignal of the wavelength λ1 to the optical wavelength converter 82connected to the port A 79.

The wavelength λ2 which is the same as that of the port B 22 in thetransmission-side optical wavelength multiplexer 10 is set in the port B80. The port B 80 receives the demultiplexed optical signal of thewavelength λ2 demultiplexed by the received-light wavelengthdemultiplexer 75 via the PD 77, and outputs the demultiplexed opticalsignal of the wavelength λ2 to the optical wavelength converter 83connected to the port B 80. In this case, the optical signal of thewavelength λ2 is generated by the optical wavelength converter 14connected to the port C 23 in the transmission side, but it is receivedby the PD 77 connected to the port B 80 in the reception side. Thus, theoptical wavelength converter 13 is incorrectly connected to the port B22 in the transmission side, which results in an erroneous reception ofthe optical signal in the reception side.

The optical wavelength converters 82 to 84 convert the demultiplexedoptical signals into the optical signals having the original wavelengthsrespectively. Specifically, the optical wavelength converter 82 convertsthe demultiplexed optical signal of the wavelength λ1 input into theport A 79, into the original wavelength which the terminal device 1 hastransmitted, and outputs the optical signal to the terminal device 1 asa destination. The port B 22 with the wavelength λ2 set therein isconnected to the incorrect optical wavelength converter 13 (whichconverts the optical signal into the wavelength λ3), and therefore, thewavelength λ2 transmitted from the terminal device 3 is input into theport B 80 in the reception side although the terminal device 2 in thetransmission side transmits the data to the terminal device 2 as adestination. Thus, the optical wavelength converter 83 converts thedemultiplexed optical signal having the wavelength λ2 into the originaloptical signal, and transmits the converted optical signal to theterminal device 2 as a destination. In the same manner as above, theoptical signal having the wavelength λ3 transmitted from the terminaldevice 2 is transmitted to the terminal device 3 as a destination.

The optical level monitor 85 temporarily stores therein and monitors theoptical power levels detected by the PDs 76 to 78. Specifically, whenthe optical power levels of the demultiplexed optical signalsdemultiplexed by the received-light wavelength demultiplexer 75 aredetected by the PDs 76 to 78 and informed respectively, the opticallevel monitor 85 temporarily stores therein and monitors the detectedoptical power levels.

FIG. 4 is a flowchart of a process of detecting the incorrect connectionin the optical wavelength multiplexing system according to the firstembodiment.

As shown in FIG. 4, in the transmission-side optical wavelengthmultiplexer 10, when the PD 24 to PD 26 detect the optical power levelsof the converted optical signals input into the ports respectively (stepS401), the optical-level monitoring controller 60 controls,respectively, the optical switches 27 to 29 connected to thecorresponding ports where the optical power levels are detected so as toinput the converted optical signals into the optical coupler 30 (stepS402).

The optical coupler 30 multiplexes all the input converted opticalsignals (step S403), and the optical branching unit 42 branches themultiplexed optical signal into the optical spectrum monitor 50 and theoptical amplifier 43 (step S404).

The optical spectrum monitor 50 detects each optical power level of thepredetermined wavelengths set in the respective ports from the branchedoptical signal (step S405).

Subsequently, the optical-level monitoring controller 60 compares eachoptical power level of the converted wavelengths detected by the PD 24to PD 26 respectively with each optical power level of the wavelengthsof the branched optical signal detected by the optical spectrum monitor50 (step S406), and determines whether there is a difference between theoptical power levels (step S407).

When it is determined that there is a difference between the two levels(“YES” at step S407), the optical-level monitoring controller 60 detectsthat any one of the optical wavelength converters is incorrectlyconnected to a port because the optical wavelength converter convertsthe optical signal into a wavelength different from the predeterminedwavelength set in the port (step S408). When there is no differencebetween the two levels, it is determined that there is no incorrectconnection between the optical wavelength converter and the port, andthe process is ended.

Effects of the first embodiment will be described next. According to thefirst embodiment, the plurality of PDs are connected to the portsrespectively, each optical power level of the converted optical signalsinput into the ports is detected, all the input converted opticalsignals are multiplexed to generate a multiplexed optical signal, aplurality of input units are provided to the ports, the convertedoptical signals input into the ports are input into the PDs, and theoptical-level monitoring controller controls the optical switches so asnot to input the converted optical signals into the optical coupleruntil the optical power levels of the converted wavelengths are detectedand so as to input the converted optical signals into the opticalcoupler when the optical power levels of the converted wavelengths aredetected.

Each optical power level of the predetermined wavelengths set in theports after being multiplexed is detected, and each detected opticalpower level of the converted wavelengths is compared with each detectedoptical power level of the wavelengths after being multiplexed. Whenthere is a difference between the two levels, it is detected that anyone of the optical wavelength converters is incorrectly connected to aport because the optical wavelength converter converts the opticalsignal to a wavelength different from the predetermined wavelength setin the port. Thus, it is possible to detect an incorrect connection andalso reduce the cost for constructing the system.

For example, by using the optical switches as input units and using theoptical coupler (CPL) as an optical signal multiplexer, the incorrectconnection in each port can be detected. Consequently, the cost forconstructing the system can be reduced as compared with the case wherean expensive arrayed waveguide grating (AWG) is employed to detect theincorrect connection. Moreover, it is possible to reconnect anincorrectly connected optical fiber cable to a proper destination and tochange the setting of a port according to a wavelength transmitted overan optical fiber cable, without stopping the system.

According to the first embodiment, the multiplexed optical signal isbranched, and each optical power level of the predetermined wavelengthsset in the ports after being multiplexed is detected from the branchedmultiplexed optical signal. Each detected optical power level of theconverted wavelengths is compared with each detected optical power levelof the wavelengths of the branched optical signal. When there is adifference in the comparison result, it is detected that a particularoptical wavelength converter is incorrectly connected to a port becausethe optical wavelength converter converts the optical signal into awavelength different from the predetermined wavelength set in the port.Therefore, the incorrect connection can be detected in the transmissionside of the optical wavelength multiplexing system, which allows furtherreduction in the cost for constructing the system.

For example, when the optical switches are used as the input units andthe optical coupler (CPL) is used as the optical signal multiplexer, anoptical signal having an incorrect wavelength due to the incorrectconnection is also multiplexed in a multiplexed optical signal.Therefore, before the multiplexed optical signal is transmitted, theincorrect connection is detected in the transmission side of the opticalwavelength multiplexing system, which allows reduction in the cost forconstructing the system and prevention of degradation in quality of themultiplexed optical signal and the optical wavelength multiplexingsystem.

In the first embodiment, the case where the incorrect connection isdetected by comparing the optical power level of the converted opticalsignal detected by the PD with that of the branched optical signalobtained by multiplexing optical signals and branching the multiplexedoptical signal is explained. However, the present invention is notlimited to this configuration. Thus, the comparison may be made betweenthe optical power level of the converted optical signal detected by thePD and the optical power level of a demultiplexed optical signalobtained by multiplexing the optical signals, branching the multiplexedoptical signal, and further demultiplexing the branched optical signalinto optical signals.

In a second embodiment, a case where the incorrect connection isdetermined by comparing optical power levels is explained with referenceto FIG. 5. Specifically, the optical power level of the convertedoptical signal detected by the PD is compared with the optical powerlevel of the demultiplexed optical signal.

FIG. 5 is a schematic of an overall configuration of an opticalwavelength multiplexing system according to the second embodiment.

Similarly to FIG. 1 according to the first embodiment, as shown in FIG.5, the optical wavelength multiplexing system according to the secondembodiment includes a transmission-side optical wavelength multiplexer,a reception-side optical wavelength multiplexer, and terminal devices,which are connected to each other by optical fiber cables so as toenable mutual communication with each other. In the transmission-sideoptical wavelength multiplexer, a plurality of optical wavelengthconverters each of which converts an input optical signal into anarbitrary preset wavelength to generate a converted optical signal areconnected to a plurality of ports (port A to port C) in whichpredetermined wavelengths are preset respectively.

Specifically, similarly to the first embodiment, wavelengths λ1 to λ3are set in the port A to port C respectively. The port A with thewavelength λ1 set therein is connected to an optical wavelengthconverter that converts an input optical signal into an optical signalof the wavelength λ1. The port B with the wavelength λ2 set therein isconnected to another optical wavelength converter that converts an inputoptical signal into the wavelength λ3. The port C with the wavelength λ3set therein is connected to still another optical wavelength converterthat converts an input optical signal into the wavelength λ2. In otherwords, the optical wavelength converters that convert input opticalsignals into wavelengths different from the wavelengths set in theconnected ports are connected to the port B and the port C,respectively.

With such a configuration, the transmission-side optical wavelengthmultiplexer controls each of optical switches 1 to 3 so as not to inputa converted optical signal into an optical coupler until the opticalpower level of the converted wavelength is detected. Specifically, theoptical wavelength converter in the transmission-side optical wavelengthmultiplexer receives the optical signal transmitted from a terminaldevice 1, converts the optical signal to an optical signal having thewavelength λ1, and outputs the converted optical signal to the port A(see (1) and (2) of FIG. 5).

In the transmission-side optical wavelength multiplexer, a plurality ofPDs connected to the ports detect the optical power levels of theconverted optical signals input into the ports respectively (see (3) ofFIG. 5). Specifically, the transmission-side optical wavelengthmultiplexer detects the optical power level of the converted opticalsignal having the wavelength λ1 input into the port A.

Subsequently, when the optical power levels of the converted wavelengthsare detected, the transmission-side optical wavelength multiplexercontrols the optical switches 1 to 3 so as to input the convertedoptical signals into the optical coupler (see (4) of FIG. 5).Specifically, when the optical power level of the converted wavelengthinput into the port A is detected, the transmission-side opticalwavelength multiplexer controls the optical switch 1 so as to input theconverted optical signal into the optical coupler.

The transmission-side optical wavelength multiplexer inputs theconverted optical signals input to the ports into the optical coupler,and multiplexes all the converted optical signals input from the portsto generate a multiplexed optical signal (see (5) and (6) of FIG. 5).Specifically, the transmission-side optical wavelength multiplexerinputs the converted optical signal having the wavelength λ1 input tothe port A into the optical coupler, causes the optical coupler tomultiplex all the input converted optical signals to generate amultiplexed optical signal, and outputs the multiplexed optical signalto the transmission-light amplifying unit.

Thereafter, the transmission-side optical wavelength multiplexerbranches the multiplexed optical signal, causes an optical wavelengthdemultiplexer (AWG) to demultiplex the branched multiplexed opticalsignal into optical signals of predetermined wavelengths set in therespective ports, and detects each optical power level of thedemultiplexed wavelengths (see (7) to (9) of FIG. 5). Specifically, thetransmission-side optical wavelength multiplexer branches themultiplexed optical signal multiplexed by the optical coupler, causesthe optical wavelength demultiplexer to demultiplex the branchedmultiplexed optical signal into wavelengths including the wavelength λ1set in the port A, and detects an optical power level of thedemultiplexed wavelength λ1.

The transmission-side optical wavelength multiplexer compares thedetected optical power level of the converted with the detected opticalpower level of the demultiplexed wavelength. When there is a differencein the comparison result, the transmission-side optical wavelengthmultiplexer detects that the optical wavelength converter is incorrectlyconnected to the port because the optical wavelength converter convertsthe optical signal into a wavelength different from the predeterminedwavelength set in the port (see (10) of FIG. 5).

Specifically, the transmission-side optical wavelength multiplexercompares the optical power level of the converted wavelength λ1 inputinto the port A with the optical power level of the demultiplexedwavelength λ1 set in the port A obtained after the multiplexed opticalsignal is branched and the wavelength λ1 set in the port A isdemultiplexed from the branched multiplexed optical signal.Subsequently, when the optical signal having the detected optical powerlevel of the converted wavelength and the optical signal having thedetected optical power level of the demultiplexed wavelength aredetermined to be those converted into the wavelength λ1, thetransmission-side optical wavelength multiplexer determines that thereis no difference between the two optical power levels and the opticalwavelength converter which converts the optical signal to the wavelengthλ1 is correctly connected to the port A with the wavelength λ1 settherein.

Similarly to the method described above, when an optical signal istransmitted from the terminal device 2, the transmission-side opticalwavelength multiplexer determines whether an optical wavelengthconverter connected to the terminal device 2 is connected to an improperport.

Specifically, the optical wavelength converter in the transmission-sideoptical wavelength multiplexer receives an optical signal from theterminal device 2, converts the optical signal into an optical signalhaving the wavelength λ3, and outputs the converted optical signal tothe port B, and the optical power level of the converted optical signalhaving the wavelength λ3 input into the port B is detected (see (11) to(13) of FIG. 5).

Thereafter, when the optical power level of the converted wavelength isdetected, the transmission-side optical wavelength multiplexer controlsthe optical switch 2 so as to input the converted optical signal intothe optical coupler, inputs the converted optical signals input to theport A and the port B into the optical coupler, and multiplexes all theconverted optical signals input from the port A and the port B togenerate a multiplexed optical signal. The transmission-side opticalwavelength multiplexer then branches the multiplexed optical signal,demultiplexes the branched multiplexed optical signal into opticalsignals having the wavelengths λ1 and λ2 which are set in the port A andthe port B respectively, and detects the optical power levels of thedemultiplexed optical signals (see (14) to (19) of FIG. 5).

The transmission-side optical wavelength multiplexer compares thedetected optical power level of the converted optical signal with thedetected optical power level of the demultiplexed optical signal. Whenthere is a difference in the comparison result, the transmission-sideoptical wavelength multiplexer detects that the optical wavelengthconverter is incorrectly connected to the port B because the opticalwavelength converter converts the optical signal into a wavelengthdifferent from the wavelength λ2 set in the port B (see (20) of FIG. 5).

Specifically, the transmission-side optical wavelength multiplexercompares the optical power level of the wavelength λ3 input into theport B after being converted thereto with the optical power level of ademultiplexed wavelength λ2 obtained after the multiplexed opticalsignal multiplexed by the optical coupler is branched and the opticalsignal having the wavelength λ2 set in the port B is demultiplexed fromthe branched multiplexed optical signal. Consequently, the optical powerlevels of different wavelengths are detected, and it is therebydetermined that there is a difference between the two optical powerlevels. Thus it is detected that the optical wavelength converter whichconverts the optical signal into a wavelength different from thewavelength λ2 set in the port B is incorrectly connected to the port B.

As explained above, the optical wavelength multiplexing system accordingto the second embodiment braches the multiplexed optical signal,demultiplexes the branched multiplexed optical signal into opticalsignals of the predetermined wavelengths set in the ports respectively,and detects each optical power level of the demultiplexed predeterminedwavelengths set in the ports, from the demultiplexed optical signals.The system compares each detected optical power level of the convertedwavelengths with each optical power level of the demultiplexedwavelengths. When there is a difference in the comparison result, it isdetected that the optical wavelength converter that converts the opticalsignal into a wavelength different from the predetermined wavelength setin a port is incorrectly connected to the port. Thus, the incorrectconnection can be detected and the cost can be further reduced.

By using an arrayed waveguide grating (AWG) as an optical wavelengthdemultiplexer which is more inexpensive than the optical spectrummonitor instead of using the optical spectrum monitor which is veryexpensive as the optical branching unit, the cost for constructing thesystem can further be reduced.

In the first embodiment, the case where the incorrect connection isdetected by comparing the optical power level of the converted opticalsignal detected by the PD with that of the branched optical signalobtained by multiplexing optical signals and then branching themultiplexed optical signal is explained. However, the present inventionis not limited to this configuration, and thus, comparison may be madebetween the optical power level of the converted optical signal detectedby the PD and the optical power level of the multiplexed optical signalafter being received.

In a third embodiment, a case where the incorrect connection isdetermined by comparing an optical power level of a converted opticalsignal detected by a PD with an optical power level of a receivedmultiplexed optical signal will be explained with reference to FIG. 6.

FIG. 6 is a schematic of an overall configuration of an opticalwavelength multiplexing system according to the third embodiment.

As shown in FIG. 6, similarly to FIG. 1 according to the firstembodiment, the optical wavelength multiplexing system according to thethird embodiment includes a transmission-side optical wavelengthmultiplexer, a reception-side optical wavelength multiplexer, andterminal devices, which are connected to each other by optical fibercables so as to enable mutual communication with each other. In thetransmission-side optical wavelength multiplexer, a plurality of opticalwavelength converters each of which converts an input optical signalinto an arbitrary preset wavelength to generate a converted opticalsignal are connected to a plurality of ports (port A to port C) in whichpredetermined wavelengths are preset respectively.

Specifically, similarly to the first embodiment, wavelengths λ1 to λ3are set in the port A to port C respectively. The port A with thewavelength λ1 set therein is connected to an optical wavelengthconverter that converts an input optical signal into an optical signalof the wavelength λ1. The port B with the wavelength λ2 set therein isconnected to another optical wavelength converter that converts an inputoptical signal into the wavelength λ3. The port C with the wavelength λ3set therein is connected to still another optical wavelength converterthat converts an input optical signal into the wavelength λ2. In otherwords, the optical wavelength converters that convert input opticalsignals into wavelengths different from the wavelengths set in theconnected ports are connected to the port B and the port C,respectively.

Settings similar to the port A to port C in the transmission-sideoptical wavelength multiplexer are provided in a port X to a port Z inthe reception-side optical wavelength multiplexer, and opticalwavelength converters that convert the optical signals into the originalwavelengths are connected to the ports respectively. Specifically, thewavelength λ1 is set in the port X, the wavelength λ2 is set in the portY, and the wavelength λ3 is set in the port Z. The port X to the port Zare connected to optical wavelength converters that convert receivedoptical signals into wavelengths used in terminal devices 1 to 3 thattransmit data (optical signals), respectively.

With such a configuration, the transmission-side optical wavelengthmultiplexer controls each of the optical switches 1 to 3 so as not toinput a converted optical signal into an optical coupler until theoptical power level of the converted optical signal is detected.Specifically, the optical wavelength converter in the transmission-sideoptical wavelength multiplexer receives the optical signal transmittedfrom the terminal device 1, converts the optical signal to an opticalsignal having the wavelength λ1, and outputs the converted opticalsignal to the port A (see (1) and (2) of FIG. 6).

In the transmission-side optical wavelength multiplexer, a plurality ofPDs connected to the ports detect the optical power levels of theconverted optical signals input into the ports respectively (see (3) ofFIG. 6). Specifically, the transmission-side optical wavelengthmultiplexer detects the optical power level of the converted opticalsignal having the wavelength λ1 input into the port A.

Subsequently, when the optical power level of the converted wavelengthis detected, the transmission-side optical wavelength multiplexercontrols the optical switches 1 to 3 so as to input the convertedoptical signals into the optical coupler (see (4) of FIG. 6).Specifically, when-the optical power level of the converted opticalsignal input into the port A is detected, the transmission-side opticalwavelength multiplexer controls the optical switch 1 so as to input theconverted optical signal into the optical coupler.

The transmission-side optical wavelength multiplexer inputs theconverted optical signals input to the ports into the optical coupler,and causes the optical coupler to multiplex all the converted opticalsignals input from the ports to generate a multiplexed optical signal(see (5) and (6) of FIG. 6). Specifically, the transmission-side opticalwavelength multiplexer inputs the converted optical signal having thewavelength λ1 input to the port A into the optical coupler, causes theoptical coupler to multiplex all the input converted optical signals togenerate a multiplexed optical signal, and outputs the multiplexedoptical signal to the transmission-light amplifying unit.

Subsequently, the transmission-side optical wavelength multiplexeramplifies the optical signal multiplexed and branched to an opticalpower level required for the transmission, and transmits the amplifiedmultiplexed optical signal to the reception-side optical wavelengthmultiplexer (see (7) of FIG. 6).

The reception-side optical wavelength multiplexer receives themultiplexed optical signal, amplifies the optical power level thereofdegraded during the transmission, and causes an received-lightwavelength demultiplexer (AWG) to demultiplex the multiplexed opticalsignal into those of respective predetermined wavelengths (see (8) ofFIG. 6). Then, the reception-side optical wavelength multiplexer detectsthe power level of the demultiplexed optical signal of the wavelength λ1as an optical power level of a received optical signal, and transmitsthe detected optical power level to an optical-level monitoringcontroller in the transmission-side optical wavelength multiplexer (see(9) of FIG. 6). Specifically, the reception-side optical wavelengthmultiplexer amplifies the received multiplexed optical signal, andcauses the received-light wavelength demultiplexer to demultiplex themultiplexed optical signal into optical signals including the opticalsignal having the wavelength λ1 set in the port X. The reception-sideoptical wavelength multiplexer detects the optical power level of thereceived optical signal having the wavelength λ1 obtained by beingdemultiplexed, and transmits the detected optical power level to theoptical-level monitoring controller in the transmission-side opticalwavelength multiplexer.

Subsequently, the optical-level monitoring controller in thetransmission-side optical wavelength multiplexer compares the detectedoptical power level of the converted wavelength with the detectedoptical power level of the received wavelength. When there is adifference in the comparison result, it is detected that the opticalwavelength converter which converts the optical signal to a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port (see (10) of FIG. 6). Specifically,the transmission-side optical wavelength multiplexer compares theoptical power level of the converted optical signal having thewavelength λ1 input into the port A with the optical power level of thewavelength λ1 after being received, obtained by being demultiplexed fromthe received multiplexed optical signal.

Then, the transmission-side optical wavelength multiplexer determinesthat the optical signal having the detected optical power level of theconverted wavelength and the optical signal having the optical powerlevel of the received wavelength are those which are converted to thewavelength λ1. Thus, it is determined that there is no differencebetween the two optical power levels and the optical wavelengthconverter which converts the optical signal to the wavelength λ1 iscorrectly connected to the port A with the wavelength λ1 set therein.

Similarly to the method described above, when the optical signal istransmitted from the terminal device 2, the transmission-side opticalwavelength multiplexer determines whether an optical wavelengthconverter connected to the terminal device 2 is connected to an improperport.

Specifically, the optical wavelength converter in the transmission-sideoptical wavelength multiplexer receives an optical signal transmittedfrom the terminal device 2, converts the optical signal into an opticalsignal having the wavelength λ3, and outputs the converted opticalsignal to the port B, and then the optical power level of the convertedoptical signal having the wavelength λ3 input into the port B isdetected (see (11) to (13) of FIG. 6).

Thereafter, when the optical power level of the converted optical signalis detected, the transmission-side optical wavelength multiplexercontrols the optical switch 2 so as to input the converted opticalsignal into the optical coupler, inputs the converted optical signalsinput into the port A and the port B into the optical coupler, causesthe optical coupler to multiplex all the converted optical signals inputfrom the port A and the port B to generate a multiplexed optical signal,and transmits the multiplexed optical signal to the reception-sideoptical wavelength multiplexer (see (14) to (17) of FIG. 6).

Subsequently, the reception-side optical wavelength multiplexer receivesthe multiplexed optical signal, demultiplexes the received multiplexedoptical signal into optical signals having the wavelengths λ1 and λ2 setin the port X and the port Y respectively, detects the optical powerlevels of the demultiplexed optical signals, and transmits the detectedoptical power levels to the optical-level monitoring controller in thetransmission-side optical wavelength multiplexer (see (18) and (19) ofFIG. 6).

The optical-level monitoring controller in the transmission-side opticalwavelength multiplexer compares the detected optical power level of theconverted optical signal with the optical power level of the receivedoptical signal. When there is a difference in the comparison result, itis detected that the optical wavelength converter which converts theoptical signal into a wavelength different from the wavelength λ2 set inthe port B is incorrectly connected to the port B (see (20) of FIG. 6).

Specifically, the optical-level monitoring controller compares theoptical power level of the optical signal after being converted into thewavelength λ3 input into the port B with the optical power level of thewavelength λ2 obtained by being received and demultiplexed, and thendetects the optical power levels of the different wavelengths. Thus, itis determined that a difference is detected between the two opticalpower levels. The transmission-side optical wavelength multiplexerdetects that the optical wavelength converter which converts the opticalsignal into a wavelength different from the wavelength λ2 set in theport B is incorrectly connected to the port B.

As explained above, according to the third embodiment, the optical-levelmonitoring controller compares the optical power level of the convertedoptical signal and the optical power level of the optical signaldemultiplexed into the predetermined wavelength from the multiplexedoptical signal received in the reception-side optical wavelengthmultiplexer. When there is a difference in the comparison result, it isdetected that the optical wavelength converter is incorrectly connectedto the port because the optical wavelength converter converts theoptical signal into a wavelength different from the predeterminedwavelength set in the port. Thus, the incorrect connection can bedetected and the cost can further be reduced.

For example, in the optical wavelength multiplexing system, themultiplexed optical signal usually used therein is received anddemultiplexed into wavelengths in one side, and each optical power levelof the demultiplexed wavelengths detected for each demultiplexedwavelength is received in the other side by feedback, and the incorrectconnection is thereby detected. Therefore, there is no need to add a newfunction to the ordinary optical wavelength multiplexing system.Accordingly, the cost can further be reduced.

In the first embodiment, the case where the optical switches are used asunits to input the converted optical signals into the optical coupler isexplained. However, the present invention is not limited to thisconfiguration, and thus variable optical attenuators (VOA) instead ofthe optical switches may be used.

In a fourth embodiment; a case where the variable optical attenuators(VOA) are used instead of the optical switches as units to input theconverted optical signals into the optical coupler will be explainedbelow with reference to FIG. 7. FIG. 7 is a schematic of an overallconfiguration of an optical wavelength multiplexing system according tothe fourth embodiment.

As shown in FIG. 7, similarly to FIG. 1 according to the firstembodiment, the optical wavelength multiplexing system according to thefourth embodiment includes a transmission-side optical wavelengthmultiplexer, a reception-side optical wavelength multiplexer, andterminal devices, which are connected to each other by optical fibercables so as to enable mutual communication with each other. In thetransmission-side optical wavelength multiplexer, similarly to the firstembodiment, a plurality of optical wavelength converters each of whichconverts an input optical signal into an arbitrary preset wavelength togenerate a converted optical signal are connected to a plurality ofports (port A to port C) in which predetermined wavelengths are presetrespectively.

Specifically, similarly to the first embodiment, wavelengths λ1 to λ3are set in the port A to port C respectively. The port A with thewavelength λ1 set therein is connected to an optical wavelengthconverter that converts an input optical signal into the wavelength λ1.The port B with the wavelength λ2 set therein is connected to anotheroptical wavelength converter that converts an input optical signal intothe wavelength λ3. The port C with the wavelength λ3 set therein isconnected to still another optical wavelength converter that converts aninput optical signal into the wavelength λ2. In other words, the opticalwavelength converters that convert input optical signals intowavelengths different from the wavelengths set in the connected portsare connected to the port B and the port C.

The optical wavelength multiplexing system according to the fourthembodiment differs from the first embodiment in that thetransmission-side optical wavelength multiplexer sets an attenuation ineach of VOAs 1 to 3 to a maximum until the optical power level of aconverted optical signal is detected, and reduces the attenuation tomake the optical power level of the optical signal to be input into theoptical coupler constant for each port, upon detection of the opticalpower level of the converted optical signal.

Specifically, similarly to the first embodiment, when an optical signalis input from the terminal device 1, the optical wavelength converter inthe transmission-side optical wavelength multiplexer converts theoptical signal into the wavelength λ1 and inputs the converted opticalsignal into the port A, and then the optical power level of theconverted optical signal received from the port A is detected in thetransmission-side optical wavelength multiplexer (see (1) to (3) of FIG.7).

When the optical power level of the converted optical signal isdetected, the transmission-side optical wavelength multiplexer controlsthe VOA 1 so as to input the converted optical signal into the opticalcoupler, and inputs the converted optical signals input to the ports,into the optical coupler. The optical coupler multiplexes all the inputconverted optical signals to generate a multiplexed optical signal, andthe optical branching unit branches the multiplexed optical signal. Thetransmission-side optical wavelength multiplexer detects each opticalpower level of the predetermined wavelengths set in the ports afterbeing multiplexed, from the branched multiplexed optical signal,compares each detected optical power level of the converted wavelengthswith each detected optical power level of the wavelengths of thebranched optical signal. When there is a difference in the comparisonresult, it is detected that the optical wavelength converter isincorrectly connected to the port A because the optical wavelengthconverter converts the optical signal into a wavelength different fromthe predetermined wavelength set in the port A (see (4) to (9) of FIG.7).

The transmission-side optical wavelength multiplexer reduces theattenuation of the VOA 1 so that the optical power level of the opticalsignal to be input into the optical coupler remains constant (see (10)of FIG. 7). Thereafter, optical signals transmitted from the terminaldevice 1 are input into the optical coupler while the attenuationthereof is gradually decreased, and the optical signals are multiplexedtherein.

Likewise, the optical power level of the wavelength λ3 of the branchedmultiplexed optical signal is detected after the optical signal inputfrom the terminal device 2 is converted into the wavelength λ3 and theoptical power level thereof is detected. Then, it is detected that theoptical wavelength converter that converts the optical signal into awavelength different from the predetermined wavelength set in the port Bis incorrectly connected to the port B (see (11) to (19) of FIG. 7). Inthis case, detection of the incorrect connection does not cause thetransmission-side optical wavelength multiplexer to reduce theattenuation of the VOA 2. When no incorrect connection is detected (whenthe optical wavelength converter is correctly connected) via the mannerdescribed above, the transmission-side optical wavelength multiplexerreduces the attenuation of the VOA 2.

As explained above, according to the fourth embodiment, the attenuationis set to the maximum until the optical power level of the convertedoptical signal is detected, and the attenuation is reduced so that theoptical power level of the input optical signal remains constant foreach port upon detection of the optical power level of the convertedoptical signal. Therefore, when the attenuation for the input opticalsignal is arbitrarily set and the input optical signal is input byattenuating the optical power level of the input optical signalaccording to the set attenuation, it is possible to prevent degradationof the quality of the multiplexed optical signal and the opticalwavelength multiplexing system. For example, multiplexing thewavelengths by keeping the optical power levels constant enables amultiplexed optical signal with higher quality to be transmitted,compared with the case where wavelengths with different optical powerlevels are multiplexed.

Although only the case of detecting the incorrect connection isexplained in the first to the fourth embodiments, the present inventionis not limited to this case. Therefore, when the incorrect connection isdetected, a user (maintenance person) may be informed about a correctconnecting destination.

In a fifth embodiment, a case where the user (maintenance person) isinformed about a correct connecting destination upon detection of theincorrect connection and an optical switch connected to the port wherethe incorrect connection is detected is turned off will be explainedbelow with reference to FIG. 8. FIG. 8 is a flowchart of a process ofdetermining the incorrect connection and a process for informing about aconnecting destination in an optical wavelength multiplexing systemaccording to the fifth embodiment.

As shown in FIG. 8, when the optical wavelength multiplexing system isstarted by the user or the like (step S801), the optical wavelengthmultiplexing system sets a connection status (STATUS [1 . . . i]) of aninput port (PORT #1 to PORT #i (maximum number of ports)) to “unset”,and sets a status of the optical switch (SW [i]) to “OFF” (step S802).The optical wavelength multiplexing system performs processes from stepsS803 to S825, which is a loop process, on ports from a port 1 to themaximum number of ports (PORT #i) (step S803).

Thereafter, the optical wavelength multiplexing system determineswhether an operating status (IS_00S [i]) of the input port (PORT #i) is“InService” indicating a service status (step S804).

When the operating status IS_00S [i] is “InService” (“YES” at stepS804), the system determines whether an input status (INDOWN [i]) of theport is “InDown” indicating an ON status (step S805).

Subsequently, when the input status (INDOWN [i]) of the port is not“InDown” (“NO” at step S805), the system determines whether theconnection status (STATUS [i]) of the PORT #i is an incorrect connection(step S806).

When the connection status (STATUS [i]) of the PORT #i is not anincorrect connection (“NO” at step S806), the system determines whetherthe connection status (STATUS [i]) of the input port (PORT #i) is“unset” (step S807).

When the connection status (STATUS [i]) of the input port (PORT #i) isnot “unset” (“NO” at step S807), the system increments [i] by one, andperforms the determination process on the next port if [i] is not themaximum number of ports (step S825).

On the other hand, when the connection status (STATUS [i]) of the inputport (PORT #i) is “unset” (“YES” at step S807), the system turns “ON”the optical switch SW [i] connected to the input-port (step S808).

Subsequently, the system determines whether an input status (AMP_INDOWN)of a light amplifying unit is “InDown” (step S809).

When the input status (AMP_INDOWN) of the light amplifying unit is“InDown” (“YES” at step S809), the system informs the maintenance person(user) of “malfunction in connection with the light amplifying unit”(step S810), sets the connection statuses (STATUS [1 . . . i]) of allthe input ports to “unset”, turns “OFF” the optical switches (SW [1 . .. i]) connected to all the input ports (step S811), and performs theprocess at step S825.

On the other hand, when the input status (AMP_INDOWN) of the lightamplifying unit is not “InDown” (“NO” at step S809), the systemdetermines whether the light input status (INDOWN) of the opticalspectrum monitor in the transmission-side optical wavelength multiplexeris “InDown” (step S812).

When it is determined that the light input status (INDOWN) of theoptical spectrum monitor is “InDown” (“YES” at step S812), the systeminforms the maintenance person (user) of “malfunction in connection withthe optical spectrum monitor” (step S813), and performs the processesfrom step S811.

On the other hand, when the light input status (INDOWN) of the opticalspectrum monitor is not “InDown” (“NO” at step S812), the systemcompares a status of an operating wavelength λ[i] in the input port witha wavelength (λx) sent from the optical spectrum monitor (step S814).

When the wavelengths λ[i] and [λx] match with each other (“YES” at stepS814), the system determines that the connection status (STATUS [i]) ofthe input port is “normal” (step S815), and informs the maintenanceperson that “the input port (PORT #i) is normal”, and performs theprocess at step S825.

On the other hand, when λ[i] and [λx] do not match with each other (“NO”at step S814), the system determines that the connection status (STATUS[i]) of the input port is “incorrect connection” (step S817).

Thereafter, the system compares an operating wavelength (λn) of an inputport (n) (n=1 to PORT_MAX (maximum number of ports)) with a wavelength[λx] sent from the optical spectrum monitor (step S818 to step S820).

When the operating wavelength (λn) and the wavelength [λx] match witheach other (“YES” at step S819), the system informs the maintenanceperson of “input port: PORT #i, destination port: PORT #n” (step S821),turns “OFF” the connected optical switch (SW [i]) (step S824), andperforms the process at step S825.

On the other hand, when the operating wavelength (λn) and the wavelength[λx] do not match with each other (“NO” at step S819), the systeminforms the maintenance person of “input port (PORT #i), operatingwavelength error between the connection wavelength (λx) and theoperating wavelength” (step S822), turns “OFF” the connected opticalswitch (SW [i]) (step S824), and performs the process at step S825.

At step S806, when the connection status (STATUS [i]) of the PORT #i isthe incorrect connection (“YES” at step S806), the system turns “OFF”the connected optical switch (SW [i]) (step S824), and performs theprocess at step S825.

Similarly, at step S805, when the input status (INDOWN [i]) of the portis “InDown” (“YES” at step S805), the system turns “OFF” the connectedoptical switch (SW [i]) (step S824), and performs the process at stepS825.

On the other hand, at step S804, when the operating status (IS_00S [i])is not “InService” (“NO” at step S804), the system sets the connectionstatus (STATUS [i]) of the input port to “unset” (step S823), andperforms the processes from step S824.

In the process at step S825, “i” is incremented one by one, and theprocesses from step S804 to step S824 are performed until “i” reachesthe maximum number “n”. When “i” reaches the maximum number “n”, thesystem ends the process.

As explained above, according to the fifth embodiment, when theincorrect connection is detected, the optical switch connected to theport is controlled so as not to input the converted optical signal intothe optical coupler. Therefore, an optical signal having a wavelengtherroneously input can be prevented from being mixed in the other opticalsignals upon multiplexing. As a result, degradation of the quality ofthe multiplexed optical signal and the optical wavelength multiplexingsystem can be prevented.

For example, when the optical switch or the VOA is used as anoptical-signal switching unit, an optical signal having incorrectlyinput wavelength also passes through the optical switch, and the opticalsignal multiplexer multiplexes optical signals including the erroneousoptical signal. Therefore, by stopping the optical-signal switching unitconnected to an incorrectly connected port, the optical signal havingerroneously input wavelength can be prevented from being mixed in theother optical signals upon multiplexing. Thus, degradation of thequality of the multiplexed optical signal and the optical wavelengthmultiplexing system can be prevented.

According to the fifth embodiment, when the incorrect connection isdetected, the predetermined wavelengths set in respective ports aresearched to detect a port as a correct connecting destination of anoptical wavelength converter which is connected to an improper port.Therefore, the incorrect connection can be detected and the port to becorrectly connected can also be specified. Thus, the burden on the userdue to an occurrence of the incorrect connection can be reduced and theincorrect connection can be promptly dealt with.

For example, when wavelengths λ1 to λ5 are set in ports 1 to 5respectively, and the port 2 is incorrectly connected with an opticalfiber cable of the wavelength λ3, it is not only detected that the port2 is incorrectly connected but also specified that the port 3 is acorrect destination of the optical fiber cable incorrectly connected tothe port 2. The detection can thereby be informed to the user, and thus,the burden on the user due to the occurrence of the incorrect connectioncan be reduced and the incorrect connection can be promptly dealt with.

Although the embodiments according to the present invention areexplained above, the present invention may be embodied in variousmanners other than the embodiments. Hence, different embodiments will beexplained below by referring to (1) the number of ports and (2) systemconfiguration.

(1) Number of Ports

For example, in the first to the fifth embodiments, the case where theoptical wavelength multiplexing system has three ports is explained.However, the present invention is not limited to this configuration, andfour ports may be provided, in other words, there is no limitation tothe number. Moreover, a plurality of optical wavelength converters maybe provided by the corresponding number of the ports so as to beconnected to the respective ports, or one optical wavelength convertermay be connected to a plurality of ports. When one optical wavelengthconverter is connected to a plurality of ports, the optical wavelengthconverter has a plurality of wavelengths set therein because differentwavelengths are set in the ports, and optical signals converted intodifferent wavelengths are thereby input into the ports respectively.

(2) System Configuration

The components of the devices shown in the drawings are functionallyconceptual, and do not always have to be physically configured as shownin the drawings. Specifically, a specific configuration in which thedevices are dispersed or integrated is not limited to the shownconfiguration. The devices may be configured by functionally orphysically dispersing or integrating all or a part of the devices inarbitrary units according to various loads or usage patterns. Forexample, the optical-level monitoring controller is divided into theinput controller and the incorrect connection detector. Furthermore, allor arbitrary portions of the processing functions performed in therespective devices may be implemented by a CPU and a program to beanalyzed and executed by the CPU, or as a hardware based on a wiredlogic.

Moreover, all or a part of the processes explained as thoseautomatically executed, such as the amplification process anddemultiplexing process of the multiplexed optical signal, of theprocesses explained in the embodiments, can be also manually executed.Alternatively, all or a part of the processes explained as thosemanually executed, such as the process for setting wavelength in eachport, can be also automatically executed using any one of known methods.Besides, information (FIG. 3, for example) including the procedure,control procedure, specific names, and various data and parameters shownin the document and the drawings can arbitrarily be changed unlessotherwise specified.

According to one aspect of the invention, the incorrect connection canbe detected and the cost for constructing the system can be reduced.

For example, by using the optical switches as the input units and usingthe optical coupler (CPL) as the optical signal multiplexer, theincorrect connection in a port can be detected. As a result, the costfor constructing the system can be reduced, compared with the case wherean expensive arrayed waveguide grating (AWG) is used to detect theincorrect connection. Moreover, it is possible to reconnect anincorrectly connected optical fiber cable to a proper destination and tochange the setting of a port according to a wavelength transmitted overan optical fiber cable, without stopping the system.

According to another aspect of the invention, the incorrect connectioncan be detected in the transmission side of the optical wavelengthmultiplexing system, and thus, the cost for constructing the system canbe further reduced.

For example, when the optical switches are used as the optical-signalswitching units and the optical coupler (CPL) is used as the opticalsignal multiplexer, an input optical signal having an incorrectwavelength due to the incorrect connection is also multiplexed in theoptical signals. By detecting the incorrect connection in thetransmission side of the optical wavelength multiplexing system beforethe transmission of the multiplexed optical signal, the cost forconstructing the system can further be reduced, and degradation of thequality of the multiplexed optical signal and the optical wavelengthmultiplexing system can be prevented.

According to still another aspect of the invention, it is possible todetect the incorrect connection and further reduce the cost.

For example, in the optical wavelength multiplexing system, a receivedmultiplexed optical signal usually used therein is demultiplexed in oneside, and each optical power level of the demultiplexed optical signaldetected for each demultiplexed wavelength is received in the other sideby feedback, and the incorrect connection is thereby detected.Therefore, there is no need to add a new function to the ordinaryoptical wavelength multiplexing system. Accordingly, the cost canfurther be reduced.

According to still another aspect of the invention, the degradation ofthe quality of the multiplexed optical signal and the optical wavelengthmultiplexing system can be prevented.

For example, multiplexing wavelengths by keeping the optical powerlevels constant allows transmission of a higher-quality multiplexedoptical signal, compared with the case where wavelengths of differentoptical power levels are multiplexed.

According to still another aspect of the invention, when optical signalsare to be multiplexed, an optical signal of an erroneously inputwavelength can be prevented from being mixed in the optical signals, andthus, the degradation of the quality of the multiplexed optical signaland the optical wavelength multiplexing system can be prevented.

For example, when the optical switch or the VOA is used as theoptical-signal switching unit, an optical signal having the erroneouslyinput wavelength also passes through the optical switch, and the opticalsignal multiplexer multiplexes optical signals including the erroneousoptical signal. Therefore, by stopping the optical-signal switching unitconnected to an incorrectly connected port, the optical signal of theerroneously input wavelength can be prevented from being mixed in theother signals upon multiplexing. As a result, the degradation of thequality of the multiplexed optical signal and the optical wavelengthmultiplexing system can be prevented.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. An optical wavelength multiplexing system comprising: a plurality ofoptical wavelength converters that convert input optical signals intoarbitrary preset wavelengths and generate converted optical signalsrespectively; a plurality of ports in which predetermined wavelengthsare preset and to which the optical wavelength converters are connectedrespectively; a plurality of first optical-power-level detectors thatare connected to the ports respectively, and detect optical power levelsof the converted optical signals input into the ports respectively; anoptical coupler that multiplexes all the converted optical signals inputfrom the ports to generate a multiplexed optical signal, the generatedmultiplexed optical signal being transmitted to a receiving device inthe optical wavelength multiplexing system and dennultiplexed intooptical signals of predetermined wavelengths; a plurality of input unitsthat are provided in the ports respectively and input the convertedoptical signals input into the ports, into the optical coupler; an inputcontroller that controls each of the input units so as not to input theconverted optical signal into the optical coupler until an optical powerlevel of the converted optical signal is detected by the firstoptical-power-level detector, and also controls each of the input unitsso as to input the converted optical signal into the optical couplerwhen the optical power level of the converted optical signal isdetected; a second optical-power-level detector that detects, from themultiplexed optical signal, each optical power level of thepredetermined wavelengths set in the ports after the converted opticalsignals are multiplexed; an incorrect connection detector that compareseach optical power level of the converted optical signals detected bythe first optical-power-level detector with each optical power level ofthe predetermined wavelengths detected by the second optical-power-leveldetector, and detects that an optical wavelength converter that convertsthe optical signal into a wavelength different from the predeterminedwavelength set in a connected port is incorrectly connected to the portwhen there is a difference therebetween in the comparison result; anoptical branching unit that branches the multiplexed optical signalmultiplexed by the optical coupler; and a multiplexed-optical-signaldemultiplexer that demultiplexes the branched multiplexed optical signalinto optical signals of the respective predetermined wavelengths set inthe ports, wherein the second optical-power-level detector detects, fromthe demultiplexed optical signals, each optical power level of thepredetermined wavelengths set in the ports after the branchedmultiplexed optical signal is demultiplexed, and the incorrectconnection detector compares each optical power level of the convertedoptical signals detected by the first optical-power-level detector witheach optical power level of demultiplexed optical signals detected bythe second optical-power-level detector, and detects that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result.
 2. An optical wavelengthmultiplexing system comprising: a plurality of optical wavelengthconverters that convert input optical signals into arbitrary presetwavelengths and generate converted optical signals respectively; aplurality of ports in which predetermined wavelengths are preset and towhich the optical wavelength converters are connected respectively; aplurality of first optical-power-level detectors that are connected tothe ports respectively, and detect optical power levels of the convertedoptical signals input into the ports respectively; an optical couplerthat multiplexes all the converted optical signals input from the portsto generate a multiplexed optical signal, the generated multiplexedoptical signal being transmitted to a receiving device in the opticalwavelength multiplexing system and demultiplexed into optical signals ofpredetermined wavelengths; a plurality of input units that are providedin the ports respectively and input the converted optical signals inputinto the ports, into the optical coupler; an input controller thatcontrols each of the input units so as not to input the convertedoptical signal into the optical coupler until an optical power level ofthe converted optical signal is detected by the firstoptical-power-level detector, and also controls each of the input unitsso as to input the converted optical signal into the optical couplerwhen the optical power level of the converted optical signal isdetected; a second optical-power-level detector that detects, from themultiplexed optical signal, each optical power level of thepredetermined wavelengths set in the ports after the converted opticalsignals are multiplexed; an incorrect connection detector that compareseach optical power level of the converted optical signals detected bythe first optical-power-level detector with each optical power level ofthe predetermined wavelengths detected by the second optical-power-leveldetector, and detects that an optical wavelength converter that convertsthe optical signal into a wavelength different from the predeterminedwavelength set in a connected port is incorrectly connected to the portwhen there is a difference therebetween in the comparison result,wherein the incorrect connection detector receives each optical powerlevel of the demultiplexed optical signals of the predeterminedwavelengths which are generated by demultiplexing the multiplexedoptical signal in the receiving device, compares the received eachoptical power level of the demultiplexed optical signals with eachoptical power level of the converted optical signals detected by thefirst optical-power-level detector, and detects that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result.
 3. An optical wavelengthmultiplexing system comprising: a plurality of optical wavelengthconverters that convert input optical signals into arbitrary presetwavelengths and generate converted optical signals respectively; aplurality of ports in which predetermined wavelengths are preset and towhich the optical wavelength converters are connected respectively; aplurality of first optical-power-level detectors that are connected tothe ports respectively, and detect optical power levels of the convertedoptical signals input into the ports respectively; an optical couplerthat multiplexes all the converted optical signals input from the portsto generate a multiplexed optical signal, the generated multiplexedoptical signal being transmitted to a receiving device in the opticalwavelength multiplexing system and dennultiplexed into optical signalsof predetermined wavelengths; a plurality of input units that areprovided in the ports respectively and input the converted opticalsignals input into the ports, into the optical coupler; an inputcontroller that controls each of the input units so as not to input theconverted optical signal into the optical coupler until an optical powerlevel of the converted optical signal is detected by the firstoptical-power-level detector, and also controls each of the input unitsso as to input the converted optical signal into the optical couplerwhen the optical power level of the converted optical signal isdetected; a second optical-power-level detector that detects, from themultiplexed optical signal, each optical power level of thepredetermined wavelengths set in the ports after the converted opticalsignals are multiplexed; an incorrect connection detector that compareseach optical power level of the converted optical signals detected bythe first optical-power-level detector with each optical power level ofthe predetermined wavelengths detected by the second optical-power-leveldetector, and detects that an optical wavelength converter that convertsthe optical signal into a wavelength different from the predeterminedwavelength set in a connected port is incorrectly connected to the portwhen there is a difference therebetween in the comparison result,wherein each of the input units has an attenuation arbitrarily settherein for each of the converted optical signals to be input into theoptical coupler, attenuates each optical power level of the convertedoptical signals according to the set attenuation, and inputs each of theattenuated optical signals into the optical coupler, and the inputcontroller sets the attenuation of each of the input units to a maximumuntil the first optical-power-level detector detects each optical powerlevel of the converted optical signals, and reduces the attenuation foreach of the ports so that optical power levels of the converted opticalsignals to be input into the optical coupler remain constant, when thefirst optical-power-level detector detects each optical power level ofthe converted optical signals.
 4. The optical wavelength multiplexingsystem according to claim 2, further comprising: an optical branchingunit that branches the multiplexed optical signal multiplexed by theoptical coupler, wherein the second optical-power-level detector detectseach optical power level, after the multiplexed optical signal isbranched, of the predetermined wavelengths set in the ports, from thebranched multiplexed optical signal, and the incorrect connectiondetector compares each optical power level of the converted opticalsignals detected by the first optical-power-level detector with eachoptical power level of the wavelengths of the branched multiplexedoptical signal detected by the second optical-power-level detector, anddetects that an optical wavelength converter that converts the opticalsignal into a wavelength different from the predetermined wavelength setin a connected port is incorrectly connected to the port when there is adifference therebetween in the comparison result.
 5. The opticalwavelength multiplexing system according to claim 1, wherein when theincorrect connection is detected by the incorrect connection detector,the input controller controls the input unit connected to the port inwhich the incorrect connection is detected so as not to input theconverted optical signal into the optical coupler.
 6. The opticalwavelength multiplexing system according to claim 1, wherein when theincorrect connection is detected, the incorrect connection detectorsearches the predetermined wavelengths set in the respective ports, anddetects a correct connecting destination port of the optical wavelengthconverter incorrectly connected to the port.
 7. An optical wavelengthmultiplexing method in an optical wavelength multiplexing system where aplurality of optical wavelength converters which convert input opticalsignals into arbitrary preset wavelengths and generate converted opticalsignals respectively, are respectively connected to a plurality of portsin which predetermined wavelengths are preset, and where the convertedoptical signals are multiplexed in a transmitting device and transmittedto a receiving device to be demultiplexed into optical signals ofpredetermined wavelengths, the optical wavelength multiplexing methodcomprising: first detecting each optical power level of the convertedoptical signals input into the ports; multiplexing, using an opticalcoupler, all the converted optical signals input from the ports togenerate a multiplexed optical signal; inputting the converted opticalsignals input into the ports for the multiplexing; controlling theinputting so as not to input the converted optical signal for themultiplexing until an optical power level of the converted opticalsignal is detected in the first detecting, and also controlling theinputting so as to input the converted optical signal for themultiplexing when the optical power level of the converted opticalsignal is detected; second detecting, from the multiplexed opticalsignal, each optical power level of the predetermined wavelengths set inthe ports after the converted optical signals are multiplexed; andcomparing each optical power level of the converted optical signalsdetected in the first detecting of each optical power level of theconverted optical signals with each optical power level of thepredetermined wavelengths detected in the second detecting of eachoptical power level of the predetermined wavelengths after the convertedoptical signals are multiplexed, and third detecting that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result; branching the multiplexed opticalsignal multiplexed by the optical coupler; and demultiplexing thebranched multiplexed optical signal into optical signals of therespective predetermined wavelengths set in the ports, wherein thesecond detecting includes detecting, from the dennultiplexed opticalsignals, each optical power level of the predetermined wavelengths setin the ports after the branched multiplexed optical signal isdennultiplexed, and the comparing includes comparing each optical powerlevel of the converted optical signals detected in the first detectingwith each optical power level of dennultiplexed optical signals detectedin the second detecting, and third detecting includes detecting that anoptical wavelength converter that converts the optical signal into awavelength different from the predetermined wavelength set in aconnected port is incorrectly connected to the port when there is adifference therebetween in the comparison result.
 8. An opticalwavelength multiplexing method in an optical wavelength multiplexingsystem where a plurality of optical wavelength converters which convertinput optical signals into arbitrary preset wavelengths and generateconverted optical signals respectively, are respectively connected to aplurality of ports in which predetermined wavelengths are preset, andwhere the converted optical signals are multiplexed in a transmittingdevice and transmitted to a receiving device to be demultiplexed intooptical signals of predetermined wavelengths, the optical wavelengthmultiplexing method comprising: first detecting each optical power levelof the converted optical signals input into the ports; multiplexing,using an optical coupler, all the converted optical signals input fromthe ports to generate a multiplexed optical signal; inputting theconverted optical signals input into the ports for the multiplexing;controlling the inputting so as not to input the converted opticalsignal for the multiplexing until an optical power level of theconverted optical signal is detected in the first detecting, and alsocontrolling the inputting so as to input the converted optical signalfor the multiplexing when the optical power level of the convertedoptical signal is detected; second detecting, from the multiplexedoptical signal, each optical power level of the predeterminedwavelengths set in the ports after the converted optical signals aremultiplexed; and comparing each optical power level of the convertedoptical signals detected in the first detecting of each optical powerlevel of the converted optical signals with each optical power level ofthe predetermined wavelengths detected in the second detecting of eachoptical power level of the predetermined wavelengths after the convertedoptical signals are multiplexed, and third detecting that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result, wherein the comparing includesreceiving each optical power level of the demultiplexed optical signalsof the predetermined wavelengths which are generated by demultiplexingthe multiplexed optical signal in the receiving device, and comparingthe received each optical power level of the demultiplexed opticalsignals with each optical power level of the converted optical signalsdetected in the first detecting, and the third detecting includesdetecting that an optical wavelength converter that converts the opticalsignal into a wavelength different from the predetermined wavelength setin a connected port is incorrectly connected to the port when there is adifference therebetween in the comparison result.
 9. An opticalwavelength multiplexing method in an optical wavelength multiplexingsystem where a plurality of optical wavelength converters which convertinput optical signals into arbitrary preset wavelengths and generateconverted optical signals respectively, are respectively connected to aplurality of ports in which predetermined wavelengths are preset, andwhere the converted optical signals are multiplexed in a transmittingdevice and transmitted to a receiving device to be demultiplexed intooptical signals of predetermined wavelengths, the optical wavelengthmultiplexing method comprising: first detecting each optical power levelof the converted optical signals input into the ports; multiplexing,using an optical coupler, all the converted optical signals input fromthe ports to generate a multiplexed optical signal; inputting theconverted optical signals input into the ports for the multiplexing;controlling the inputting so as not to input the converted opticalsignal for the multiplexing until an optical power level of theconverted optical signal is detected in the first detecting, and alsocontrolling the inputting so as to input the converted optical signalfor the multiplexing when the optical power level of the convertedoptical signal is detected; second detecting, from the multiplexedoptical signal, each optical power level of the predeterminedwavelengths set in the ports after the converted optical signals aremultiplexed; and comparing each optical power level of the convertedoptical signals detected in the first detecting of each optical powerlevel of the converted optical signals with each optical power level ofthe predetermined wavelengths detected in the second detecting of eachoptical power level of the predetermined wavelengths after the convertedoptical signals are multiplexed, and third detecting that an opticalwavelength converter that converts the optical signal into a wavelengthdifferent from the predetermined wavelength set in a connected port isincorrectly connected to the port when there is a differencetherebetween in the comparison result, wherein each of the inputtingincludes, using an attenuation arbitrarily set therein for each of theconverted optical signals to be input into the optical coupler,attenuating each optical power level of the converted optical signalsaccording to the set attenuation, and inputing each of the attenuatedoptical signals into the optical coupler, and the controlling includessetting the attenuation of each of the inputting to a maximum until thefirst detecting detects each optical power level of the convertedoptical signals, and reducing the attenuation for each of the ports sothat optical power levels of the converted optical signals to be inputinto the optical coupler remain constant, when the first detectingdetects each optical power level of the converted optical signals.